ERU2 – Winter 2015: Andrew’s Results

4 dollars and some patience gives you a working spectrometer!

The Summary

To keep things short, what I would like to say first is that it turns out with some patience, a $3 webcam, a broken DVD, some cardboard, and a bit of image processing, you can produce a fully functioning absorbance spectrometer. The project was a success, but is far from over. Currently images are taken from the webcam and processed to extract spectral data, which is functional but inefficient. The next step is to produce a software package that can be used to calibrate the spectrometer, collect data, and analyse the results (peak identification and fitting). That being said, the system is currently fully functional and was even used to examine the absorbance properties of some household items. The model is shown in the image to the right.

The Working Model

The working model is very simple, using LEDs for the light source, a clear container for the sample chamber, a cardboard slit to block off the light properly for diffraction from the clear layer of a DVD reflected towards the $3 web camera. The spectras were taken as follows:

  1. Image is taken with empty container inserted.

  2. Container is filled with a sample (fruit punch and ground and strained spinach were used as tests) and inserted back into the spectrometer.

  3. A second image is taken with the sample containor.

  4. Using imageJ and the two images as grayscale 32 bit type images, an absorbance image was produced using the image calculator as: (image from 3 – image from 1) / image from 3.

  5. A profile plot of the spectra was taken and exported to csv to be plotted using Python.

An example of the spectras obtained is shown below. As you can see, they are not calibrated, but do follow the expected curve shapes for photosynthetic material and a red dye. The plotted spectrums are shown below.

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Concluding Remarks

With this demonstration, I hope it is clear that there really is very little limit to DIY devices in the era we live in. The technology and information is widely available, all that is needed is a small investment, some patience, and some very expensive devices can be made accessible where the funds don’t exist. Where do I see the role of the $4 spectrometer? It may not be in high zoot chemistry labs, but there is a need for this type of device in teaching labs and could bring research grade theory to highschools in a hands on setting, an invaluable experience in my opinion. In addition, it could be used for when precision and accuracy are not that important. It is not always the case that a high resolution spectra is required and with the cost of equipment absurdly high, it would be advantageous for alternative cheaper options to research grade equipment.

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